One solution for cover up the oops could be the tape that is used to cover adjoining sheets of luan wall panelling *if* you can get in a matching color. The tape is about an inch wide.
One easy way to find the backers is by using a magnet. Some folks have used a piece of wood, plywood or even sheet metal to span a couple of studs. You may not have studs if you have a fiberglass sided FW tho.
I like RV Oscar rivets for securing heavy things. They're a type of blind rivet and have a high holding power. They'd work if you use a piece of sheet metal on the wall and then rivet that to the wall and mount the TV to that. Just paint the sheet metal a color of your choice to blend in.
What you do will depend on the size and weight of the TV and whether or not you're using an articulating mount.
